1. Field of the Invention
The present invention relates to a laminated composite electronic device constructed with different kinds of ceramic layers, such as magnetic ceramic and dielectric ceramic layers, and in particular, to a laminated composite electronic device combining an inductance portion, in which internal electrodes are formed in a spiral shape in the laminated magnetic ceramic layers, with a capacitor portion, in which a pair of internal electrodes opposing each other are formed within the laminated dielectric ceramic layers.
2. Description of Prior Art
In manufacturing electronic devices of a laminated composite type, there are available two kinds of methods for obtaining a laminated body, one of which is so-called slurry build method and the other of which is so-called sheet method. In the slurry build method, magnetic paste and electric conductive paste are printed over one another by a method such as screen printing so as to form the magnetic material layers and an internal electrode pattern having a spiral shape therein, and a dielectric paste and the electrically conductive paste are also printed over one another to form the dielectric material layers and a pair of internal electrode patterns opposing each other therein. In the sheet method of the latter, the magnetic ceramic green sheets on which the internal electrode patterns are printed in the spiral shape with the electric conductive paste in advance by the screen printing method are stacked, and the dielectric sheets on which the opposing internal electrodes are printed with the electrically conductive paste in advance are also stacked. The internal electrode patterns formed on the magnetic ceramic green sheets are connected one by one in the spiral shape via electrical conduction by means of so-called through-holes which are also provided on the magnetic ceramic green sheets in advance.
The laminated body which is obtained by either one of the methods mentioned above is ultimately baked, and the electrically conductive paste is also baked after being printed on both side surfaces on which the electrically conductive bodies are exposed to form external electrodes thereon. In this manner, the laminated composite electronic device can be obtained. Inside of the laminated body obtained in this manner, the magnetic material layers and the dielectric material layers are stacked or laminated as a unit. Further, in the magnetic material layers is formed the coil-shaped internal electrode stacked spirally in a direction of lamination thereof, and a part of the internal electrode is connected to the external electrode at an edge portion of the laminated body mentioned above. Further, in the dielectric material layers, at least one pair of internal electrodes are formed opposed to each other through the same layer(s), and those internal electrodes are extended or led out to the opposing edge surfaces of the laminated body to be electrically connected to the external electrodes, respectively. In this manner, the inductor and the capacitor are connected in a predetermined condition through the external electrodes.
Such a laminated composite electronic device, in the manufacturing process thereof, is made by baking the laminated body of the different kinds of ceramic layers at a high temperature, in the condition of joining them together and is cooled down thereafter.
However, there are cases that the different kinds of ceramics have respective thermal expansion rates which are greatly different from each other, in particular, such as between the magnetic ceramic layers and the dielectric ceramic layers. Then, because of the differences in the thermal expansion or shrinkage between the respective ceramic layers of the laminated body formed by baking, thermal stresses occur inside of the laminated body during a cooling process after the baking, thereby distorting the laminated body in shape and causing cracks inside of it.
Conventionally, there is proposed a means for preventing the thermal stress in the cooling process after the baking, such that a ceramic layer(s) combining the compositions of the magnetic ceramic layers and the dielectric ceramic layers is inserted between them.
However, even by combining the different kinds of ceramics, it is not necessarily possible to obtain a ceramic having an expected thermal expansion rate, therefore, it is not enough to prevent the laminated body fully from distorting in the shape thereof during the cooling process after the baking.